Method of producing electric gaseous discharge device



Oct. 6, 1935. T, FOULKE 2,056,664

METHOD OF PRODUCING ELECTRIC GASEOUS DISCHARGE DEVICES Filed Sept. 6, 1955 5TEEP WAVE FRONT 5OURCE 12 INVENTOR Jed 8. C9owf C ATTORNEY Patented Oct. 6, 1936 UNITED STATES METHOD OF PRODUCING ELECTRIC GASEOUS DISCHARGE DEVICES Ted E. Foulke, Nutlty, N. J., assignor to General Electric Vapor Lamp Company, Hoboken, N. J., a corporation of New Jersey Application September 6, 1935, Serial No. 39,480

2 Claims.

The present invention relates to electric gaseous discharge devices, .and particularly to discharge devices of the cathode .glow type.

A particular object of the invention is to provide a novel method of producing an evenly activated cathode within an electric gaseous discharge device having a dissimilar anode. Still other objects and advantages of my invention will appear from the following detailed specification 1o or from an inspection of the accompanying drawing.

The invention consists in the new and novel steps of the method, as hereinafter set forth and claimed.

15 For low Voltage operation it is essential that the cathode of a cathode glow lamp should be coated with a substance of low work function, such as barium strontium or the like. In my Patent 1,965,589, granted July 10, 1934, I have de- 20 scribed a method of producing a coating using these substances which has a lower work function and a longer life than is obtainable with any other known method. In using this method, however, it was found that the best results were 35 attained with devices having two electrodes of substantially equal area, since in some cases where the electrodes are of greatly dissimilar area objectionable dark blotches occasionally appear on the surface of the larger electrode, rendering 30 the device unmarketable as a lamp.

I have now discovered that these blotches on the electrode are invariably avoided by the novel step of simultaneously treating two lamps, with reversed connections, on the same steep wave 35 front source. With this novel method the current from the source divides between the lamps asymetrically on different half cycles, in accordance with the respective surface areas of the electrodes, the current density on each of the 40 coated electrodes thus being that necessary to produce complete and uniform activation thereof. As a result I have found that these novel lamps always operate with a smooth velvety glow over the entire electrode surface, regardless of how dissimilar are the electrode areas.

For the purpose of illustrating my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which Fig. 1 is an elevational view in part section of a do lamp having an activated cathode which greatly exceeds the area of the anode, and

Fig. 2 is a schematic diagram of the circuit by which this type of lamp is preferably activated.

As particularly shown in Fig. 1 of this drawing my novel lamp has a sealed vitreous envelope having a reentrant stem 2 through which there are sealed the two inleads 3 and 4. The inlead 3 is directly connected to the lower end of a tubular cathode 5 of nickel or the like which extends axially within said envelope l. A wire 6 5 of nickel, iron, or other suitable metal which constitutes the anode is welded at one end to the inlead 4 and thence extends outwardly and then upwardly parallel to the cathode 5 to a point beyond the end of said cathode, thence across the 10 end of said cathode and again downwardly parallel to the opposite side of said cathode, the free end of said anode preferably being bent inwardly and sealed into the stem 2 in order to increase the rigidity of the structure. Opposite the end of the cathode 5 said anode 6 is likewise preferably wound about an insulator l which is suitably supported by a wire 8 welded to the end of the cathode 5 in order to maintain the desired relationship between the cathode 5 .and the anode. The separation of these electrodes is, of course, determined by the breakdown potential desired, being of the order of A of an inch in the present case. A suitable base 9 of conventional design is affixed to the envelope I, the inleads 3 and 4 being connected to a pair of terminals on said base. Said lamp contains any suitable gaseous atmosphere, such as a mixture of neon with .4% argon at a pressure of the order of m. m. of mercury. 30

In the manufacture of this lamp the central portion of the exterior surface of the tubular cathode 5 is coated with a substance of low work function while the bands ID at either end of said cathode 5 are preferably coated with an antiglow material. As disclosed in my patent, previously referred to, the active coating is preferably produced by first spraying or otherwise coating the cathode 5 with a mixture of barium and strontium carbonates or other similar compound or compounds, together with a suitable binder, such as nitrocellulose, and any suitable vehicle, such as ethyl acetate. The end bands I are at this time similarly coated preferably with powdered aluminum with the same binder and vehicle. The electrode assembly is then sealed into the envelope l and said envelope thoroughly exhausted, after which the cathode 5 is heated, as by an induction furnace, to a temperature sufiicient to decompose the carbonates to the oxide, the gas being exhausted as evolved. During this heating the binder is, of course, reduced to carbon. The desired gaseous atmosphere is then admitted and the device sealed off.

Up to this point the procedure is the same as in the patent referred to hereinbefore. As the next step, however, the inleads 3 and 4 of two similar lamps are connected with the leads II and I2, but in a reverse manner, as shown in Fig. 2. Said leads II and I2 are in turn connected to any suitable source (not shown) of steep Wave front oscillations, such as produced by the discharge of an inductance through a condenser during the period of primary circuit interruption. This source causes a discharge within each of the lamps of sufficient energy to break up a portion of the barium oxide coating, leaving barium which is cemented to the electrode surface by an oxygen and barium oxide band. This bombardment of the cathodes 5 is carried on until there is a uniform corona thereon. During this bombardment the aluminum cleans up any excess oxygen which is evolved.

Due to the fact that two lamps are connected simultaneously, but with reversed polarity, complete and uniform activation of the barium surface is invariably produced on a cathode whose area greatly exceeds that of the anode, due to the fact that the current flowing from the source divides unequally between the lamps, and varies in each lamp as the polarity of the source is reversed. As a result the current density of the discharge bombarding each cathode is always of substantially the optimum value for proper reduction of the oxide surface, despite the wide dissimilarity in the area of the electrodes. Thus the black, unactivated spots which may in some cases occur when a single lamp with such unequal electrode areas is treated alone on the steep wave front source are now completely eliminated due to the automatic variation in current in each lamp which is provided by the novel simultaneous activation of two lamps on a single source.

While I have described my invention by reference to certain structures and steps of the method employed therewith, it is to be understood that my invention is not limited thereto, but that various omissions, changes and substitutions, within the scope of the appended claims, may be made therein Without departing, from the spirit of my invention.

I claim as my invention:

1. The method of activating the electrode surfaces of electric gaseous discharge devices having alkaline earth coated cathodes whose area differs from that of the anodes thereof which comprises simultaneously connecting a pair of said devices with reverse polarity to a source of steep wave front oscillations, whereby the current divides unequally between said lamps on any half cycle.

2. The method of producing electric gaseous discharge devices having electrodes of dissimilar areas which comprises coating one of the electrodes of each device with a reducible oxygen compoundof an alkaline metal, heating said electrodes in vacuo to a temperature sufficient to decompose said compound to the oxide, providing a gaseous atmosphere about the electrodes in each device, simultaneously connecting a pair of said devices with reversed polarity to a single source of steep wave front oscillations to produce a discharge therein of sufficient energy to reduce said oxide to the metal, and availing of the parallel connection of said devices to divide the current from said source unequally on any half cycle in accordance with the area of the negative electrodes, whereby said coated surfaces are uniformly reduced by said discharge.

TED E FOULKE. 

